Pressure-sensitively adhesive products based on acrylates are known from the prior art. Their chemicals resistance makes acrylate-based adhesives especially suitable for bonding in industrial applications. A disadvantage of the known compositions, however, is that their use on substrates having surfaces of low energy (“low surface energy” materials, also LSE materials hereinafter) is difficult. This difficulty is manifested on the one hand in the bond strength of the known pressure-sensitive adhesives (PSAs) on non-polar substrates such as polypropylene or such as steel coated with LSE varnish, and also, on the other hand, in the speed with which the maximum bond strengths are achieved. The principal cause of the low bond strengths of known acrylate-based PSAs on non-polar surfaces is considered to be the difference in the surface energies of the known polymer compositions and the LSE materials, and also the absence of suitable points of attachment within the LSE surfaces for covalent or strongly non-covalent bonds. Accordingly, the adhesion between known acrylate-based polymer compositions and LSE surfaces is based essentially on relatively weak van-der-Waals forces.
One approach to the development of higher bond strengths between LSE surfaces and polymer compositions based on polyacrylates lies in the use of tackifier resins. Another approach uses primers, i.e. adhesion promoters, in order to raise the surface energy of the LSE substrates. While the use of primers is fundamentally costly and inconvenient, the use of tackifier resins leads to a decrease in the cohesion of the polymer composition, possibly leading in turn to fracture of the bond under load. Such loss of cohesion is especially critical when the polymer composition in question is used for the bonding of articles which are subject to particular forces, such as vibrations, for example. Corresponding vibrations are observed with components in the automotive sector, particularly in the area of the body or in the engine compartment.
Numerous new developments in the area of paints and varnishes on which temporary or permanent attachment of adhesive tapes is required are producing a desire, particularly in the automotive sector, for adhesive tapes which have good bond strengths even on non-polar surfaces, without any compromises on cohesion having to be accepted. Such PSAs ought, moreover, to exhibit good chemicals resistance and to develop high bond strengths after just a short time. Adhesive tapes furnished with such PSAs ought, furthermore, to have a low weight, in order to take account of the rising requirements for low fuel consumption in the motor vehicle sector. In order to reduce the volume weight of adhesive tapes, acrylate-based foam carriers have been proposed in the past.
One example of an adhesive tape including a layer of an acrylate-based foam carrier of this kind is described in EP 2 226 369 A1. The adhesive tape described therein, however, comprises a PSA based on a chemically crosslinked rubber, and therefore the resistance towards chemicals such as petroleum spirit, for example, is not adequately ensured.
While the use of acrylate-based adhesives would increase the chemicals resistance by comparison with rubber-based adhesives, simply switching the rubber PSA for an acrylate-based PSA carries the likelihood of the above-described problems on LSE materials. Using tackifier resins to improve the bond strengths of the acrylate-based PSAs, however, is not appropriate particularly in the automobile sector, on account of the above-described vibrations. Over time, moreover, it would be likely that the tackifying resin used would migrate from the PSA into the acrylate-based foam carrier layer, leading to an additional loss in the bond strengths over time. The alternative approach known from the prior art, i.e. the use of primers, is likewise out of the question for practical reasons on surface areas of motor vehicles.
Against this background there is a fundamental demand for multilayer products which exhibit good bond strengths on non-polar surfaces without any need to accept compromises in terms of cohesion. Multilayer products ought further to exhibit good chemicals resistance, develop high bond strengths after just a short time, possess a low weight, and retain the high bond strengths over long periods.
The present invention is based on the object, accordingly, of providing an improved multilayer product.